Acceleration sensor

Abstract

An acceleration sensor having movable and stationary electrodes electrically insulated from each other in a reliable manner to improve the accuracy and sensitivity in the detection of acceleration. The acceleration sensor includes an upper substrate (1) of a low resistivity silicon material, a lower substrate (2) of an insulating material provided under the upper substrate (1), and an insulating groove (5) perforating the upper substrate (1) completely from the upper to lower side thereof and around the entire periphery of a support beam (4) in the upper substrate (1). By using the upper substrate (1), stationary blocks (6) are formed separately on the opposite sides of the support beam (4) in confronting relation therewith. As a result, the support beam (4) and the stationary blocks (6), each being formed of the same low resistance material, are electrically insulated from each other by the insulating groove (5). An acceleration signal is produced on the basis of a variation in electrostatic capacitance across movable and stationary electrodes, which are constituted by a mass portion (4C) of the support beam (4) and each of the stationary blocks (6).

What is claimed is: 
     
       1. An acceleration sensor comprising: a first substrate formed of a silicon material which is used as a conductive material;   a second substrate provided on the lower side of said first substrate and electrically insulated from the first substrate;   said first substrate including; a support beam having a mass portion forming capacitive electrodes for displacement in a parallel direction to a surface of said second substrate according to the degree of acceleration, a fixed portion for fixing said support beam to said second substrate and a support portion for intermediately supporting said mass portion to said fixed portion,   an insulating groove extending through a thickness of said first substrate around the entire periphery of said support beam, and stationary blocks forming capacitive electrodes defined by said insulating groove on the outer sides of said support beam separately across said insulating groove and fixed to said second substrate;     gap means forming a gap space in order to space said mass portion and said support portion from a surface of said second substrate; and   said second substrate being separated from said first substrate by an insulating layer which is at least provided on the lower side of said fixed portion and stationary blocks.   
     
     
       2. An acceleration sensor as defined in claim 1, wherein said insulating groove defines a narrow detection groove between said mass portion of said support beam and each of said stationary blocks, and movable and stationary electrodes are formed on lateral side surfaces of said support beam and said stationary blocks in face to face relation with each other across said detection groove. 
     
     
       3. An acceleration sensor as defined in claim 1, wherein said support beam is securely fixed to said second substrate at said fixed end, and reduced in a width in said support portion to provide at least one support for said mass portion in a fore free end portion to be displaced horizontally according to the degree of acceleration in the fashion of at least one fulcrum point type acceleration sensor. 
     
     
       4. An acceleration sensor as defined in claim 3, wherein, in order to prevent said mass portion on said support beam from contacting said stationary blocks, said second substrate is provided with stopper portions in positions on the opposite sides of the fore end of said mass portion, thereby delimiting the amount of displacement of said support beam. 
     
     
       5. An acceleration sensor according to claim 3, wherein said width of said support portion is smaller than a thickness of said fixed portion and said support beam provides a cantilever type support. 
     
     
       6. An acceleration sensor as defined in claim 1, wherein said first substrate is formed of silicon material with a (110) crystal face. 
     
     
       7. An acceleration sensor according to claim 6, wherein said first substrate is formed of a n-type silicon material. 
     
     
       8. An acceleration sensor as defined in claim 1, wherein said second substrate is selected from the group consisting of a glass and a vitreous material and bonded to the lower side of said first substrate through a glass layer. 
     
     
       9. An acceleration sensor according to claim 1, wherein said second substrate is formed of a silicon material having a surface covered with an insulating oxidation film. 
     
     
       10. An acceleration sensor according to claim 1, wherein each of said stationary blocks further comprises a detecting stationary block for detecting an electrostatic capacitance and a driving block for producing an electrostatic force for the support beam. 
     
     
       11. An acceleration sensor comprising: a substrate which is selected from the group consisting of an insulating material and oxidized semiconductor material;   a support beam which includes a mass portion forming a predetermined mass and first capacitive electrodes on side surfaces of said mass portion, a fixed portion for fixing said support beam to said substrate and a thin support portion for intermediately connecting between said mass portion and said fixed portion;   a pair of stationary blocks arranged on both sides of said support beam separately across an air gap and fixed to said substrate, said stationary blocks provided with second capacitive electrodes on the opposite sides of first capacitive electrodes of said mass portion;   gap means forming a gap space in order to space said mass portion and thin support portion from a surface of said substrate; and   said mass portion being displaced in a parallel direction to the surface of said substrate according to the degree of acceleration and said support beam and stationary blocks formed of a silicon material which is used as a conductive material and electrically insulated from said substrate.   
     
     
       12. An acceleration sensor according to claim 11, wherein said gap means is formed of an insulating layer at least between said substrate and said fixed portion of the support beam and said stationary blocks. 
     
     
       13. An acceleration sensor according to claim 12, wherein said insulating layer is glass and said substrate is selected from the group consisting of a glass and a vitreous material, and the lower side of said fixed portion of the support beam and said stationary blocks are bonded to said substrate through said insulating layer. 
     
     
       14. An acceleration sensor according to claim 11, wherein movable and stationary electrodes are formed on lateral side surfaces of said mass portion and said stationary blocks in face to face relation with each other across said air gap. 
     
     
       15. An acceleration sensor according to claim 11, wherein a width of said thin support portion is smaller than a thickness of said fixed portion. 
     
     
       16. An acceleration sensor according to claim 11, wherein said substrate is provided with stopper portions in positions on the opposite sides of said mass portion, thereby preventing said mass portion of said support beam from contacting said stationary blocks. 
     
     
       17. An acceleration sensor according to claim 11, wherein said support beam and stationary blocks are formed of a n-type silicon material with a (110) crystal face. 
     
     
       18. An acceleration sensor according to claim 11, wherein said substrate is formed of a vitreous material. 
     
     
       19. An acceleration sensor according to claim 11, wherein said substrate is formed of a silicon material having a surface covered with an insulating oxidation film. 
     
     
       20. An acceleration sensor according to claim 11, wherein each of said stationary blocks is formed of a detecting stationary block for detecting an electrostatic capacitance and a driving block for producing an electrostatic force for said support beam.